The standard method used to refine, for example, raw sugar to levels acceptable for marketing as white sugar and/or use in food products is through crystallization methods. Less practiced methods include ion exchange, chemical precipitation or carbon absorption. Raw sugar usually includes sugar in crystalline form produced from sugar cane, and may be in a moist or in a liquid form where taken from a refining process prior to crystallization or in liquid form by dissolving raw sugar in crystalline form in water.
As an example only, a source of sugar is sugar cane. Harvested sugar cane typically is sent to a raw sugar mill. The sugar cane is processed in a shredder to break apart the cane and rupture juice cells. Rollers extract sugar juice from the fibrous material, typically called bagasse. The bagasse may be recycled as a fuel for the mill boiler furnaces, or can be used as a raw materials source for the production of chemicals such as furfural and ethanol. It is also used in the production of fibrous materials such as wood products and paper, and as animal feedstuffs.
Sugar juice is purified before concentration by boiling in an evaporator. The concentrated juice or syrup is concentrated further and seeded with small sugar crystals in a crystallization process. Sugar crystals are grown to a required size by adding syrup during boiling. A syrup is separated from these raw sugar crystals in centrifugals, and a molasses is typically left over from the final centrifuging. This raw sugar from the centrifugals typically is dried and transferred for storage.
A current practice of certain industrial scale food and/or beverage producers that utilize sugar is, for economic reasons, to purchase a high purity sugar product on the market from time to time that is in a form not yet suitable for use in food production, because such sugar product, e.g., contains impurities such as color and ash components. Such producers, while saving cost in purchasing such sugar for food and/or beverage production, usually also desire a whiter appearing sugar for their use in food and/or beverage production. Raw sugar, for example, while substantially pure in sucrose, typically is not considered fit for direct use as food or a food ingredient due to the impurities it ordinarily contains. As stated, high purity sucrose material such as raw sugar currently has been purified by non-chromatographic processes such as a process utilizing affination in which raw sugar is mixed with hot concentrated syrup to soften outer coating crystals, which are then separated from syrup by centrifugation. Crystals are discharged from the centrifuge and dissolved in hot water to form a sugar liquor.
The melted sugar liquor is purified with either a carbonation or phosphatation process which traps suspended impurities in larger particles that are easier to separate from the sugar liquor. Carbonatation adds carbon dioxide and lime to melted sugar to form a precipitate of calcium carbonate. Carbonatation precipitate is removed, for instance, by pressure filtering sugar liquor through cloth in a pressure leaf filter, leaving a straw-colored, crystal clear liquid. Phosphatation adds phosphoric acid to melted sugar and removes precipitate as a layer from a flotation clarifier. Phosphatated liquor is generally filtered through sand in a deep bed filter to remove residual precipitate left after clarification. This liquid then passes through decolorizing columns which adsorb the colorant molecules. A clear liquid is concentrated by boiling in a vacuum pan, and then seeded with fine sugar crystals and grown to a desired size by adding liquor. When crystals are a desired size, crystals and syrup are discharged from the pan. The mixture of crystals and syrup is processed in centrifuges where crystals are separated from syrup. Separated syrup is boiled again and more sugar crystals are extracted from it, and repeated. Refined sugar crystals are dried by tumbling them through a stream of air, then graded and packaged. Other purification methods include sulfitation processes and processes known as Talofoc and Talodura processes which use phosphotation and cationic surfactants or polyacrylaimides for color removal.
Industrial applications of chromatographic separations are typically applied to a feedstock in order to separate constituents present in significant quantities. For example, a commonly practiced application of chromatography in the sugar industry is to recover sugar from molasses. Sugar in molasses, which makes up approximately 60% of the dissolved solids, is separated from non-sugars that make up the remaining 40% of the dissolved solids.
U.S. Pat. No. 4,412,866 describes an example of the operation of chromatographic simulated moving bed (or sometimes called “SMB”) method to separate the components of a feed stock. A resin bed is divided into a series of discrete vessels, each of which functions as a zone within a circulation loop. A manifold system connects the vessels and directs, in appropriate sequence to (or from) each vessel, each of the four media accommodated by the process. Those media are generally referred to as feed stock, eluent, extract and raffinate, respectively. As applied to a sugar factory, a typical feed stock is a lower purity sucrose solution, the eluent is water, the extract is an aqueous solution of sucrose and the raffinate is an aqueous solution containing nonsucrose, such as salts and high molecular weight compounds. The simulated moving bed disclosed by the '866 patent is of the type sometimes referred to as a “continuous SMB.”
An example of a batch chromatographic method is described in the disclosure of U.S. Pat. No. 4,359,430, which utilizes sucrose feedstocks derived from sugar beets at purities of approximately 7% to 60% sucrose. See also, e.g., U.S. Pat. No. 5,466,294, which utilizes a “soft raw syrup” as a feedstock to a chromatographic method which is not in a high purity form at a less than 89% purity sucrose on a dry solids basis, i.e., approximately 11% non-sucrose impurities.